The day before, cook the potatoes for the Rösti in water until almost done. Drain, quench and let cool.
The next day, wash and quarter the tomatoes for the ragout. Peel shallots and garlic and dice finely. Fry them in olive oil in a pan. Add the tomatoes and season with salt and pepper. Simmer at low heat for 5-8 minutes, then remove from heat and keep warm.
For the Rösti, meanwhile, peel and coarsely grate the potatoes. Slice the parmesan into shavings. Mix with the potatoes in a bowl and season with salt and pepper. Heat clarified butter in a large pan. Form 8 portions from the potato and cheese mixture, place in the pan and fry for 3-4 minutes on each side. Take them out and let them drip off on kitchen paper.
Wrap each tenderloin with 1 slice of ham and season with a little salt and pepper. Fry in a pan in hot oil for 1-2 minutes on each side. Then add butter. Remove from the heat, leave to stand for 4 minutes and repeatedly pour butter over them. Serve the tomato ragout with rösti and sirloin.